The present invention relates to a fiberscope device such as an endscope or the like, and more particularly, to a eyepiece for such a device.
A fiberscope, as is well known in the art, includes a bundle of many optical fibers each having a diameter of the order of microns, an objective lens at the front end of the bundle, and an eyepiece lens at the rear end. An image of the object being observed is formed on the entrance end face of the optical fiber bundle at the front end thereof and passes through the fiber bundle to the exit end face at the rear end thereof where the image is observed through the eyepiece lens. Each of the optical fibers forming the optical fiber bundle, as shown in FIG. 1, has a core 1a for transmitting light, and a cladding 1b surrounding the core 1a which transmits substantially no light. When a number of optical fibers 1 are bundled by applying adhesive to the claddings, the cores 1a are arranged at intervals p as shown in the enlarged diagram of FIG. 2. That is, the cores 1a are separated from one another, and a dark region 1c is formed between the cores 1a. When the exit end face of the optical fiber bundle is observed through the eyepiece lens, the presence of the regularly arranged cores 1a and the dark region 1c results in fixed-pattern optical noise, as a result of which the image cannot be clearly observed. In FIG. 2, reference numeral 2 designates the field-of-vision frame of the eyepiece device.
FIG. 3 shows an optical intensity distribution formed by the cores 1a and the dark region 1c. In the optical intensity distribution, parts corresponding to the cores 1a have a certain optical intensity, and parts corresponding to the dark region 1c are zero in optical intensity. The optical intensity difference between the core 1a and the dark region 1c is a. The optical intensity distribution over the image under observation, that is, the arrangement pattern noise of the cores 1a and the dark region 1csuperimposed on the object's image, lowers the apparent resolving power and is a factor causing eye fatigue in the observer. Furthermore, in a still photographing operation, the resolving power is apparently lowered significantly because the image is at rest. On the other hand, in a television photographing operation, interference occurs between the optical fiber bundle and the color separating filter of the television image pickup tube or television scanning lines causing a moire pattern interference in the reproduced image, thus making it difficult to observe the image clearly under certain conditions. The same moire pattern is observed when a shared observation type telescope is coupled to the fiberscope
Many efforts have been made to solve the above-described problems. The conventional approaches are directed to a reduction of the diameter of the individual optical fiber 1 or the thickness of the cladding 1b. However, since the amount of reduction of the diameter of the optical fibers or the cladding thickness is limited, problems remain.
In order to prevent the formation of such a moire pattern, a comb-type filter or a trap circuit has been provided in the television image pickup section or in the television image receiver section. However, this method is extremely ineffective in preventing the formation of the moire pattern in an apparatus such as an endscope having a special arrangement pattern.